At least 12 people, including three Turkish police officers, were killed in separate incidences overnight in southeast Turkey.

The officers died after Kurdistan Workers Party (PKK) militants detonated a bomb near a police armored vehicle as it traveled along a highway in southeast Turkey, according to security sources. Another officer was seriously wounded in the attack in the Nusaybin district of Mardin province when explosives planted on the road were detonated by remote control. Police set up checkpoints across the district as they sought the assailants.

Meanwhile, PKK fighters were killed by Turkish security forces in separate clashes elsewhere in the mainly Kurdish region, which has been besieged by conflict since a ceasefire broke down in July, upending a peace process launched in 2012.

In Siirt province, attack helicopters took off from a military base and launched attacks on militants in the Eruh district while Sikorsky helicopters landed commandos on surrounding hills, the sources said. Six PKK fighters were killed in clashes.

Elsewhere in the province, three militants were killed as they tried to infiltrate a base in the Pervari district, triggering a fight with soldiers there, the sources added.

The PKK, designated a terrorist group by Turkey, the United States, and the European Union, launched its separatist insurgency in 1984; more than 40,000 people have been killed in the conflict.

Fighting has intensified in the run-up to the November 1 parliamentary election, in which Prime Minister Recep Tayyip Erdogan's ruling AK Party hopes to restore its majority.

The insurgency has reportedly killed more than 40,000 people over three decades. Erdogan said this month that some 2,000 PKK militants had been killed since the conflict resumed in July. Around 100 members of Turkish security forces have been killed, based on information from government officials and security sources.